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require File.expand_path('../../../spec_helper', __FILE__)
describe "Array#repeated_combination" do
before :each do
@array = [10, 11, 12]
end
it "returns an enumerator when no block is provided" do
@array.repeated_combination(2).should be_an_instance_of(Enumerator)
end
it "returns self when a block is given" do
@array.repeated_combination(2){}.should equal(@array)
end
it "yields nothing for negative length and return self" do
@array.repeated_combination(-1){ fail }.should equal(@array)
@array.repeated_combination(-10){ fail }.should equal(@array)
end
it "yields the expected repeated_combinations" do
@array.repeated_combination(2).to_a.sort.should == [[10, 10], [10, 11], [10, 12], [11, 11], [11, 12], [12, 12]]
@array.repeated_combination(3).to_a.sort.should == [[10, 10, 10], [10, 10, 11], [10, 10, 12], [10, 11, 11], [10, 11, 12],
[10, 12, 12], [11, 11, 11], [11, 11, 12], [11, 12, 12], [12, 12, 12]]
end
it "yields [] when length is 0" do
@array.repeated_combination(0).to_a.should == [[]] # one repeated_combination of length 0
[].repeated_combination(0).to_a.should == [[]] # one repeated_combination of length 0
end
it "yields nothing when the array is empty and num is non zero" do
[].repeated_combination(5).to_a.should == [] # one repeated_combination of length 0
end
it "yields a partition consisting of only singletons" do
@array.repeated_combination(1).sort.to_a.should == [[10],[11],[12]]
end
it "accepts sizes larger than the original array" do
@array.repeated_combination(4).to_a.sort.should ==
[[10, 10, 10, 10], [10, 10, 10, 11], [10, 10, 10, 12],
[10, 10, 11, 11], [10, 10, 11, 12], [10, 10, 12, 12],
[10, 11, 11, 11], [10, 11, 11, 12], [10, 11, 12, 12],
[10, 12, 12, 12], [11, 11, 11, 11], [11, 11, 11, 12],
[11, 11, 12, 12], [11, 12, 12, 12], [12, 12, 12, 12]]
end
it "generates from a defensive copy, ignoring mutations" do
accum = []
@array.repeated_combination(2) do |x|
accum << x
@array[0] = 1
end
accum.sort.should == [[10, 10], [10, 11], [10, 12], [11, 11], [11, 12], [12, 12]]
end
describe "when no block is given" do
describe "returned Enumerator" do
describe "size" do
it "returns 0 when the combination_size is < 0" do
@array.repeated_combination(-1).size.should == 0
[].repeated_combination(-2).size.should == 0
end
it "returns 1 when the combination_size is 0" do
@array.repeated_combination(0).size.should == 1
[].repeated_combination(0).size.should == 1
end
it "returns the binomial coeficient between combination_size and array size + combination_size -1" do
@array.repeated_combination(5).size.should == 21
@array.repeated_combination(4).size.should == 15
@array.repeated_combination(3).size.should == 10
@array.repeated_combination(2).size.should == 6
@array.repeated_combination(1).size.should == 3
@array.repeated_combination(0).size.should == 1
[].repeated_combination(0).size.should == 1
[].repeated_combination(1).size.should == 0
end
end
end
end
end
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